Multiplanar ultrasonic vascular imaging device, system incorporating same, method of use and protective sheath

ABSTRACT

An apparatus, method, system, component kit and protective sheath for cannulation of blood vessels are disclosed. The apparatus comprises a sensor assembly to provide ultrasound images of at least one blood vessel in a portion of a patient&#39;s body in two perpendicular planes. The sensor assembly may have graphic markings on an exterior surface thereof to facilitate orientation of the sensor assembly on the patient and guidance of a needle towards a desired target vessel during the cannulation procedure. The sensor assembly may also include associated structure to cooperate with a reference location element to place, align and secure the sensor assembly to the patient&#39;s skin at a desired location.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/072,662,filed Feb. 5, 2002, now U.S. Pat. No. 6,755,789, issued Jun. 29, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the cannulation of veins andarteries under the guidance of ultrasound.

2. State of the Art

Insertion of catheters into central veins or arteries can be a difficulttask because the vein or artery may be located deep within the body ormay otherwise be difficult to access in a particular patient. Multipleattempts at penetration may result in extreme discomfort to the patientand loss of valuable time during emergency situations. Furthermore,central veins and arteries are often in close proximity to each other.While attempting to access the internal jugular vein, for example, thecarotid artery may instead be punctured, resulting in severecomplications or even mortality due to consequent blood loss due to thehigh pressure of the blood flowing in the artery.

To prevent complications during catheterization, it is known thatultrasonic instruments can be used to determine the location anddirection of the vessel to be penetrated. Various approaches use aDoppler-only technique with no imaging. One such technique transmitsultrasonic waves via a transducer from the skin surface to the vessel.Due to the flow of blood in the vessel, or the pulsation of the vascularwalls, the ultrasonic wave undergoes a Doppler shift effect, whichcauses the reflected signal to be at a frequency different from thetransmitted signal. The frequency difference between the transmitted andreceived signals is then converted to an electrical signal, amplifiedand sent to an audio speaker. The frequency of the tone emitted from thespeaker increases as the frequency difference becomes greater,indicating the approximate location of the vessel. Improvements to thistechnique place either the transmitting transducer, receivingtransducer, or both transmitting and receiving transducers within ahollow needle, so that the audio signal becomes louder as the needle isturned towards a vessel within the patient's body. While suchapplications are helpful in guiding the needle towards the generallocation of vessels, the obtainable accuracy is obviously limited. Otherlimitations of this technology include difficulty distinguishing veinsfrom nearby arteries, difficulty determining when the vessel has beenpenetrated, and difficulty implementing the known Seldinger technique.

Other conventional approaches to identification of vessel location anddirection use two-dimensional ultrasound imaging to either mark thevessel location on the skin before attempting to access the vessel usingthe known Seldinger technique or view the vessel as the needle tipadvances towards it. See British Journal of Anaesthesia, 822–6 (1999).However, it would be desirable to improve ultrasound imaging techniquesfor the cannulation of blood vessels to make the use of such technologyless cumbersome and more accurate.

BRIEF SUMMARY OF THE INVENTION

The present invention uses ultrasound techniques in an improved methodand apparatus for cannulation of blood vessels. In contrast toconventional approaches, the present invention provides a clinician withthe ability to manipulate the needle during insertion with both handswhile observing the progress of the needle toward and into the desiredtarget vessel in substantially real time.

The apparatus of the invention comprises a sensor assembly including twoultrasonic, linear transducer arrays, each comprising a plurality ofactive imaging transducer elements, the arrays being orientedperpendicularly to each other to form a “T” configuration and carried bya housing. The 90° relative orientation of the array axes provides theability to quickly and easily image blood vessels in both thelongitudinal and transverse planes as a needle with attached catheter isguided towards a target vessel. One advantage of the present inventionis that the needle operator may accurately orient the needle withrespect to the target vessel and may, as desired, monitor the needle atall times as it passes through the anterior wall of the vessel. Thus,this technique and apparatus may eliminate the need to insert the first,or seeker, needle used in the Seldinger technique and greatly increasethe accuracy over Doppler-only techniques where the needle operator isguided solely by an audible tone. Again, it is notable that theclinician employing the present invention is enabled to manipulate theneedle during insertion with both hands while simultaneously observingthe progress of the needle toward and into the desired target vessel.

In other embodiments of the present invention, the sensor assembly maybe used in combination with a protective sheath having a frame elementassociated therewith and a cover configured to encompass the sensorassembly and bearing graphics to provide means, in cooperation with theframe element, for orienting the sensor assembly and securing the sensorassembly to the patient's body in a desired orientation.

In still another embodiment of the invention, the sensor assembly mayinclude a housing configured to include two laterally extendingprotrusions or “wings” proximate the lower edges of two opposing sidewalls, the wings each carrying a magnet thereon. This embodiment of thesensor assembly may be employed in combination with a reference locationelement in the form of a dielectric (such as a polymer) film or tapebearing an adhesive on one side thereof for attachment to the skin of apatient over the general location of the blood vessel to be cannulated,the tape including two laterally spaced shims of a magneticallyresponsive metal or polymer. The lateral spacing of the shimsapproximates that of the magnets, but the shims are somewhat larger thanthe magnets to permit the sensor assembly to be moved about by theclinician over a limited area of the patient's body with respect to thefilm to precisely locate the sensor assembly. The magnets, in turn,permit such movement but exhibit magnetic fields robust enough tomaintain the sensor assembly in place when it is released by theclinician.

In still a further embodiment of the invention, the housing of thesensor assembly may be configured for use with a reference locationelement in the form of an elongated ribbon having an adhesive coating ateach end thereof, the ribbon being adhered to the skin of the patient.The ribbon extends through a slot in the sensor assembly housing, whichhas associated therewith at least one resilient gripping element whichmay be manipulated by the clinician to release tension on the ribbon toenable sliding of the sensor assembly therealong as well as limitedrotation thereof with respect to the ribbon to precisely locate thesensor assembly. When a desired location of the sensor assembly isreached, then the at least one resilient gripping element is releasedand the sensor assembly is fixed in place.

In further embodiments of the present invention, the sensor assemblyfurther includes at least one ultrasonic Doppler transducer element usedto transmit and receive a single ultrasonic beam at an angle relative tothe imaging transducer array in the longitudinal plane. The addition ofthe Doppler transducer element or elements provides directional bloodflow and blood velocity information with regard to the target vessel andothers nearby and thus improves the ability to distinguish veins fromarteries. The directional information from the Doppler transducerelement or elements may be converted to a color mark with one distinctcolor indicating blood flow in one direction and another distinct colorindicating blood flow in the opposite direction. For example, when thesensor housing is appropriately aligned on the body with respect tocover markings depicting blood flow toward and away from the heart,blood flow toward the heart may be indicated with the color blue andblood flow away from the heart may be indicated with the color red.Thus, when the single color scan line is overlaid on top of a grayscalelongitudinal image of a possible target vessel on a monitor screen, ablue mark on the color screen will indicate a vein and a red mark willindicate an artery. While an array of Doppler elements may also be usedto provide a full-color image, a single Doppler beam reduces thecomplexity and cost of providing desired directional flow information.

In still another embodiment, the Doppler transducer element or elementscarried by the sensor housing may be configured to transmit and receive“chirped” ultrasound pulses to obtain Doppler information at discretedepths within the body. A pulse is chirped if its carrier frequencychanges with time. This frequency modulation, or frequency sweeping,causes the Fourier spectrum of the chirped pulse to broaden. Thus, adigital signal processor may be used to analyze the reflected signal viaa Fast Fourier Transform (“FFT”) algorithm to separate distances ordepths of various features within the body. The phase change betweentransmitted and received signals is used to determine speed anddirection of flow in the blood vessels.

In yet another embodiment, two pulsed Doppler elements may be used fordetermining speed and direction of flow in the blood vessels. In thisembodiment, the two pulsed Doppler elements each comprise a group ofactive imaging transducer elements included in one of the linearultrasonic transducer arrays, specifically the array hereinafter termeda “longitudinal” array, which is to be positioned in use over thevessels to be detected and substantially parallel thereto. The twopulsed Doppler elements, each comprising a contiguous group of activeimaging transducer elements, are mutually spaced from each other alongthe length of the array and are each angled at the same but relativelyopposing angle to a perpendicular to the plane of the array of whichthey are a part. The two pulsed Doppler elements each transmit andreceive ultrasonic signals, by which blood flow direction and velocitymay be determined.

Yet another aspect of the present invention comprises a protectivesheath into which the sensor assembly may be inserted, a packagingconfiguration therefor and a method of use thereof. The protectivesheath comprises an elongated tubular thin polymer film element, closedat one end and open at the other. The protective sheath may be taperedso as to be of larger diameter or transverse dimension at the open endthan at the closed end thereof. The open end of the protective sheath isfolded back over the rest of the protective sheath so that a portioncomprising about one-half of the protective sheath is inside-out, oreverted, and extends over the remaining portion thereof. The end of thenow-everted protective sheath now open and defining a bore extending tothe closed end of the sheath (the original or first open end of theprotective sheath now lying adjacent and surrounding the original closedend due to eversion) is rolled outwardly back upon itself toward theclosed end until only a small “pouch” or “foot” of a size suitable forreceiving the sensor assembly remains, the doubled and rolled polymerfilm forming a toroidal shape defining a mouth of the pouch or foot. Atthat juncture, the skirt of material defining the now-everted originalor first open end of the protective sheath is folded back over theoutside of the toroidal shape of rolled polymer film. In use, theinventive protective sheath may be placed in a tray of a kit includingother sterile, disposable elements of the present invention with itsmouth defined by the skirt and toroidal shape of rolled polymer filmfacing upward. In use, the sensor assembly (which is not sterile) may beplaced into the pouch or foot through the mouth and the folded-backskirt of the protective sheath grasped and pulled proximally along thecable extending to the sensor assembly to maintain sterility of theexterior of the protective sheath while encompassing the nonsterilesensor assembly and associated cable therein for use. Tabs of anothermaterial may be secured to the skirt to facilitate visual identificationand grasping of the skirt.

Methods of vessel identification, a system incorporating the sensorhousing of the present invention and a kit of disposable sterilecomponents are also encompassed by the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A and 1B respectively comprise a bottom schematic view and a sideschematic view of a first exemplary sensor assembly of the presentinvention;

FIG. 2 is an exploded schematic view of the sensor assembly of FIGS. 1Aand 1B disposed within a transparent, protective sheath and with ahousing cover according to the present invention;

FIG. 3 comprises an exemplary dual-panel ultrasound image provided bythe apparatus of the present invention of a patient's neck in twoimaging planes as a needle is guided towards the internal jugular veinfor cannulation;

FIG. 4 comprises an exploded, detailed view of one exemplaryimplementation of a sensor assembly of the present invention employed incombination with a ribbon-type reference location element;

FIG. 5 is a block diagram of an exemplary system for the cannulation ofblood vessels incorporating a sensor assembly of the present invention;

FIG. 6 is a block diagram of one embodiment of exemplary Dopplerprocessing hardware for “chirped” Doppler suitable for use in the systemof FIG. 5;

FIG. 7A is a block diagram of another embodiment of exemplary Dopplerprocessing hardware for a first approach to “pulsed” Doppler suitablefor use in the system of FIG. 5;

FIG. 7B is a block diagram of yet another embodiment of exemplaryDoppler processing hardware for a second approach to “pulsed” Dopplersuitable for use in the system of FIG. 5;

FIG. 7C is a schematic side elevation of a longitudinal imagingtransducer array, wherein groups of active imaging transducer elementsthereof are employed as Doppler elements in association with thecomponents of FIG. 7B;

FIGS. 8A through 8D respectively comprise a top elevation, a frontalelevation, a side elevation and a perspective view of another exemplaryimplementation of a sensor assembly according to the present inventionfor use with a magnetic reference location element;

FIGS. 9A through 9D respectively comprise a top elevation, a frontalelevation, an enlargement of a portion of the frontal elevation and aperspective view of a magnetic reference location element suitable foruse with the sensor assembly embodiment of FIGS. 8A through 8D; and

FIGS. 10A through 10D schematically depict a protective sheath andmanipulation thereof for packaging and use, according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A and 1B comprise a schematic illustration of a sensor assembly10 in accordance with the present invention. The sensor assembly 10includes a housing 12 containing a first linear, ultrasonic elongatedcross-sectional or transverse transducer array 14 and a second linear,ultrasonic elongated longitudinal transducer array 16; which arrays 14and 16 are placed perpendicular to one another. Transducer arrays 14 and16 as assembled with housing 12 form a “T” shape and are employed toobtain ultrasonic images of potential target blood vesselssimultaneously in both the transverse and longitudinal planes.Transverse transducer array 14 defines the head of the “T,” whilelongitudinal transducer array 16 defines the body thereof. Transducerarrays 14 and 16 each extend linearly and include a plurality ofmutually adjacent piezoelectric active imaging transducer elements fortransmitting and receiving ultrasonic waves, as will be understood byone having skill in the field of the present invention. However, whilethe two linear transducer arrays 14, 16 are described and depicted asarranged in a “T” configuration, it is contemplated that any arrangementplacing arrays 14, 16 in mutually perpendicular relationship is suitableand encompassed by the present invention.

In addition to transducer arrays 14 and 16, one embodiment of theapparatus of the present invention includes a “chirped” Dopplertransducer element 18 for transmitting and receiving a single ultrasonicDoppler beam 22 in alignment with the longitudinal transducer array 16and at incident angle φ, for example, about 20° to about 30°, to aperpendicular to the patient's skin underlying housing 12. The Dopplertransducer element 18 provides blood flow direction and velocityinformation as an additional feature to aid the clinician indistinguishing veins from arteries during cannulation. The Dopplertransducer element 18 includes one semicircular piezoelectrictransmitter Tx for generating the Doppler beam and one semicircularpiezoelectric receiver Rx for receiving the reflected Doppler beam. Theorientation and relative alignments of Tx and Rx may be as shown in FIG.1A, or rotated ±90° or ±180°, as desired. Alternatively, if a “pulsed”Doppler transducer element is employed, only a single circularcombination emitter and receiver element is required. Further, whileDoppler transducer element 18 is shown as having a concave face in FIG.1B, a planar or convex face is also suitable. An attached ultrasoniclens may also be employed. It will be readily recognized that whilemultiple transmitters and receivers may be employed to acquire Dopplerinformation corresponding to the entire ultrasound scan and imageproduced by longitudinal transducer array 16, using a single beam toproduce Doppler information corresponding to a single scan linetraversing the target blood vessel will provide all required directionalblood flow information necessary for safe vessel cannulation and at farless complexity and cost.

By way of example only, manufacturers of custom medical gradetransducers, such as may be suitable for use in implementing the presentinvention include Acoustic Imaging Transducers of Phoenix, Ariz.;Krantkramer of Lewistown, Pa. and Blatek, Inc. of State College, Pa.

The sensor assembly 10 of the present invention further includes amulti-conductor cable 20, which enters housing 12 at one side thereofand is operably coupled to the cross-sectional on transverse transducerarray 14, the longitudinal transducer array 16, and the Dopplertransducer element 18. Also, in order to increase the efficiency of theDoppler transducer element 18 and to reduce reflections in gap area orcavity 24 created by incident angle φ of Doppler beam 22, gap area 24may be filled with a material such as an epoxy or polymer, which issubstantially acoustically matched to bodily tissue. Suitable compoundsinclude, without limitation, PMMA, PTFE, and RTV silicone available, forexample and not by way of limitation, from 3M Corporation, Minneapolis,Minn. and DuPont, Wilmington, Del. Of course, gap area or cavity 24 mayalso be filled with an acoustic transmission gel, or be partially filledwith an epoxy or polymer and partially filled with an acoustictransmission gel.

FIG. 2 and FIG. 3 below illustrate a first, schematically illustrated,exemplary sensor assembly according to the present invention in thecontext of a technique for using the present invention for cannulationof the internal jugular vein located in the neck of a human patient.However, it will be apparent that the apparatus and method described mayalso be used to identify and access various blood vessels within amammalian subject's body. FIG. 2 is a schematic illustration of thesensor assembly 10 as described with reference to FIGS. 1A and 1B and asviewed from above looking down on cover 30 in use with an elongated,flexible, protective and preferably transparent sheath 44 and areference location element in the form of an elongated ribbon 42 bearingan adhesive at each end thereof to form an ultrasonic cannulationassembly 48. Cover 30 is graphically marked and configured to aid in theuse of the sensor assembly 10 for the cannulation of blood vessels. Theelongated, flexible, protective, transparent sheath 44 provides aprotective enclosure for the sensor assembly 10 for use in a sterilefield within an operating room. One suitable elongated, flexible,protective, transparent sheath for use with the present invention isoffered commercially by Protek Medical Products, Inc. of Iowa City,Iowa, while another, more preferred embodiment of protective sheath 44is described herein.

In this embodiment, the elongated, flexible, protective, transparentsheath 44 extends from a relatively larger, open end to a relativesmaller, closed end to form a tapered, flaccid and thus highly flexibletubular enclosure with a frame element 46 bonded to the interior surfaceof the narrower, closed end thereof. The elongated, flexible,protective, transparent sheath 44, cover 30, and adhesive ribbon 42comprise a disposable kit of sterile components for use with thisembodiment of the invention and are discarded once each cannulationprocedure is complete. The sensor assembly 10 may thus be reused withoutsterilization for new procedures with a new kit of disposable itemsincluding the protective, transparent sheath 44, cover 30, and adhesiveribbon 42.

Prior to use, conventional acoustic transmission gel is placed insidethe elongated, flexible, protective, transparent sheath 44 within thearea defined by the frame element 46 to provide efficient acousticcoupling between the material of the sheath 44 and the sensor assembly10 secured to the frame element 46. After disposition of the acousticgel, the sensor assembly 10 is inserted into the protective, transparentsheath 44 and housing 12 snapped into the frame element 46, themulti-conductor cable 20 being aligned with the longitudinal axis of theelongated, flexible, protective, transparent sheath 44 and extending toand through an opening at the opposite, wider end thereof for connectionto a monitoring device. Next, the cover 30 is placed over the housing 12of sensor assembly 10 from the exterior of the protective, transparentsheath 44 and then engaged with the frame element 46 to tighten thecover 30 over the sensor assembly 10. After applying additional acoustictransmission gel to the patient's skin in the area to be accessed, theultrasonic cannulation assembly 48 is placed on the patient's body inorder to obtain ultrasound images of a target blood vessel.

Cover 30 bears orientation markings on its exterior surface indicatingblood flow towards the heart 36 and away from the heart 38 to assist inproper orientation of sensor assembly 10 on the patient's body. Forexample, if attempting to cannulate the internal jugular vein of theneck, the sensor assembly 10 of the ultrasonic cannulation assembly 48would be placed on the patient's neck with the arrow depicted inorientation marking 36 pointing towards the patient's heart and thearrow depicted in orientation marking 38 pointing towards the patient'shead. Proper orientation of the ultrasonic cannulation assembly 48ensures that information concerning blood flow direction obtained fromthe Doppler transducer element 18 correctly indicates whether apotential target vessel is a vein or an artery.

Cover 30 also contains slots 35 (FIG. 4) through which the adhesiveribbon 42 may pass to secure the ultrasonic cannulation assembly 48 tothe skin of the patient for hands-free operation thereof during thecannulation procedure. The adhesive ribbon 42 contains an area ofadhesive material on the bottom (skin contact) side toward each endthereof, leaving the center region of the adhesive ribbon 42 free ofadhesive material where it comes into contact with the ultrasoniccannulation assembly 48. A suitable adhesive is a 1526 tape adhesiveoffered by 3M Corporation, Minneapolis, Minn. Thus, after orienting theultrasonic cannulation assembly 48 on the patient's body and obtainingan ultrasound image of the vessel to be accessed (see FIG. 3), theadhesive ribbon 42 is adhered to the skin at both sides of sensorassembly 10. Further, the cover 30 contains resilient, movable grippingelements such as portions of a compressible spring, clip (not shown inFIG. 2), extending about the sides thereof to grip the adhesive ribbon42 when engaged therewith and create tension on both ends of theadhesive ribbon 42 to hold the ultrasonic cannulation assembly 48tightly against the skin. Further, by disengaging the gripping elements,ribbon tension is released and the ultrasonic cannulation assembly 48may be easily moved from side to side or rotated at a slight angle untilthe optimum ultrasound image is obtained, at which juncture the grippingelements are re-engaged with adhesive ribbon 42 to secure sensorassembly 10 in place.

Cover 30 bears transverse grid markings 32, longitudinal grid markings34 and a notch-like needle guide 40, which are used in combination tohelp guide the needle towards the vessel to be accessed. The transversegrid markings 32 are aligned parallel to transverse transducer array 14and centered with respect to the head of the “T,” while the longitudinalgrid markings 34 are aligned parallel to longitudinal transducer array16 and over the body of the “T.” The needle guide 40 is alignedlongitudinally with the body of the “T” and is adjacent the head endthereof. The notch of the needle guide 40 is aligned with a like notchof the frame element 46 to allow clear passage of the needle to the skintissue underlying sensor assembly 10 without perforation of elongated,flexible, protective, transparent sheath 44 and possible compromise ofthe sterile field. After the optimum ultrasound image of the vessel isobtained through manipulation of sensor assembly 10 secured to frameelement 46 and within protective, transparent sheath 44 and theultrasonic cannulation assembly 48 is secured to the patient asdescribed above, a needle with catheter attached is inserted into thetissue at a location defined by the needle guide 40. The needle is thenguided towards the target vessel location, which is visually ascertainedin relation to transverse grid markings 32 comprising letters A throughE and longitudinal grid markings 34 comprising numerals 1 through 5 aswill be hereinafter described. The method of guiding the needle towardsthe vessel using transverse grid markings 32 and 34 will become moreapparent in the discussion of FIG. 3 which follows.

FIG. 3 is a representation of a dual-panel ultrasound image 50 generatedby the monitoring system used with ultrasonic cannulation assembly 48 inthe method of the present invention for the cannulation of bloodvessels. The dual-panel ultrasound image 50 includes a transverse image51 and a longitudinal image 53 of the neck displayed simultaneously insubstantially real time on a single screen using known split-screen orpicture-in-picture technology. The transverse image 51 is obtained fromthe transverse transducer array 14 of the sensor assembly 10 of FIGS. 1Aand 1B and comprises a transverse image 51 of the internal jugular vein56 and a transverse image 51 of the adjacent carotid artery 58. Alsoshown is a transverse grid display 52, which corresponds to thetransverse grid markings 32 (letters A through B) on cover 30 of FIG. 2.Stated another way, transverse grid markings 32 are keyed to transversegrid display 52. The transverse grid display 52 and the transverse gridmarkings 32 indicate the relative location of the needle insertion pointto the vessel to be punctured. For example, a needle inserted throughthe needle guide 40 of FIG. 2 would enter the tissue at a locationproximate C relative to sensor assembly 10 on the transverse gridmarkings 32. However, FIG. 3 shows that the cross-sectional image of theinternal jugular vein 56 is approximately laterally between B and C andthat the cross-sectional image of the carotid artery 58 correspondsalmost directly to C of the cross-sectional grid display 52. Therefore,in order to avoid the carotid artery 58 and access the internal jugularvein, the sensor assembly 10 would be moved laterally until internaljugular vein 56 is directly below C on cross-sectional grid display 52.

Similarly, the longitudinal image 53 is obtained from the longitudinaltransducer array 16 of the sensor assembly 10 of FIGS. 1A and 1B anddisplays a longitudinal image of the internal jugular vein 56 and animage of the skin surface 64. If the carotid artery 58 is substantiallydirectly below internal jugular vein 56, carotid artery 58 will also beshown, as depicted in FIG. 3. In addition, a needle image 66 mayoptionally be displayed to show the location of the needle tip 66T as itpasses from the skin surface 64 through the tissue toward thelongitudinal image of the internal jugular vein 56. Thus, the needleimage 66 provides the clinician with a precise indication of impendingneedle entry through a vessel wall. The imaging method may be used witha needle designed to enhance the image of the needle tip by plating orotherwise treating the needle tip surface with a material that is highlyreflective of ultrasonic waves, such needles being known in the art andbeing termed “echogenic.” One such needle employs a tip dipped inpolymer, including gas bubbles therein, providing a diffuse rather thanspecular reflection. Also shown is a longitudinal grid display 54, whichcorresponds to the longitudinal grid markings 34 on cover 30 of FIG. 2.Stated another way, longitudinal grid markings 34 are keyed tolongitudinal grid display 54. The longitudinal grid display 54 and thelongitudinal grid markings 34 indicate the relative longitudinallocation of the needle to the target blood vessel as it passes throughthe tissue under sensor assembly 10 in a manner analogous to the exampleabove for the transverse grid display 52 and the transverse gridmarkings 32.

FIG. 3 also includes an example of how blood flow information isindicated to the user of the preferred embodiment of the presentinvention. As discussed above, the Doppler transducer element 18 ofFIGS. 1A and 1B provides blood flow information to help distinguishveins from arteries within a patient's body. In FIG. 3, blood flowdirection indicators 68 and 70 represent a means of providing visuallyperceptible indicia to identify blood flow direction in correspondencewith longitudinal image 53. In the embodiment of FIGS. 1A and 1B, asingle scan line of Doppler information obtained from the Dopplertransducer element 18 is overlaid on top of the longitudinal image 53.The preferred method of distinguishing blood flow direction between twopotential target vessels, one direction of blood flow depicted byindicator 68 and blood flow in the opposite direction depicted byindicator 70, is to display indicators 68 and 70 in two distinctlydifferent colors. For example, a color coding scheme may be defined suchthat deoxygenated blood flow in veins corresponds to the color blue andoxygenated blood flow in arteries corresponds to the color red. Thus,blood flowing towards the heart in the longitudinal image of theinternal jugular vein 56 could be indicated by displaying indicator 68in blue while blood flowing towards the head in the longitudinal imageof the carotid artery 58 could be indicated by displaying indicator 70in red. This color coding scheme is also carried over to the orientationmarkings 36 and 38 on cover 30 of FIG. 2. Thus, in the present example,orientation marking 36 would be blue to further indicate blood flowingtowards the heart and orientation marking 38 would be red to furtherindicate blood flowing towards the head. The inventors recognize thatany combination of colors, including variations in gray-scale shading,may be used to indicate blood flow direction and such variations areencompassed by the present invention. Further, it is recognized thatmany other methods of indicating blood flow direction may be usedincluding, but not limited to, displaying on transverse image 51 orlongitudinal image 53 symbols, patterns, letters, or words correspondingto distinct blood flow directions. Also, blood flow direction may beindicated for the sake of simplicity by displaying only one indicatorcorresponding to either blood flow towards or away from the heart. Bloodflow velocity may also be calculated from the signals sent and receivedby Doppler transducer element 18.

FIG. 4 depicts a more detailed implementation of the sensor assembly 10depicted in FIGS. 1A, 1B and 2. Elements and features previouslyidentified with respect to FIG. 2 are identified by the same referencenumerals in FIG. 4. Linear transducer arrays 14 and 16 and Dopplertransducer element 18 are shown disposed in housing 12, multi-conductorcable 20 entering housing 12 through a cutout 21 in the sidewallthereof. An array housing lid 112 having protrusion 114 secures the endof multi-conductor cable 20 in cooperation with cutout 21, the sidewallof the housing 12 and the protrusion 114 gripping multi-conductor cable20 in annular slot 23. Cover 30, also termed a “shell,” is configured toconformally extend over housing 12 and the bottom end thereof isconfigured to engage frame element 46 (not shown in FIG. 4) in asnap-fit fashion, housing 12 being trapped therebetween. Riser 120extends upwardly from the main body of cover 30 and includes a pluralityof gripping elements 122 on each side thereof to assist gripping ofriser 120 by the fingers of the clinician. Slots 35 extend through eachside of riser 120, and adhesive ribbon 42 (shown above cover 30 in FIG.4 for clarity) extends through slots 35 and to either side of cover 30.A resilient gripping element in the form of spring clip 124 extendsabout the lower periphery of cover 30 in engagement with slots 126 and128, the crossed ends 130 of spring clip 124 having loops 132. When in arelaxed position, the side rails 134 of spring clip 124 snugly clampadhesive ribbon 42 against the sidewalls of cover 30. However, whenloops 132 are pressed toward each other, as by using the thumb andforefinger, side rails 134 are pushed away from the sidewalls of cover30, permitting sensor assembly 10 to be slid back and forth and rotatedsomewhat with respect to adhesive ribbon 42, the latter due to a slotelongation greater than the width of the adhesive ribbon 42.

As shown in FIG. 5, a monitoring system 74 includes a multi-elementultrasonic beamformer (also termed “processing board”) 76 and Dopplerhardware 86 (see FIG. 6 for detail) of sensor assembly 10 operablycoupled to the multi-conductor cable 20 of the sensor assembly 10 ofFIGS. 1A and 1B. Further, the monitoring system 74 includes a dualB-mode digital scan converter 78 coupled to the beamformer 76, asuitably programmed host computer 80, such as a personal computer, and adisplay device 82, which may comprise a cathode ray tube (CRT) monitor.Other types of monitors, such as LCD touch screen monitors, or TFTmonitors, may also be employed. Suitable beamformers and scan converterboards are available, for example, from B–K Medical of Copenhagen,Denmark; Analogic, Inc. of Peabody, Massachusetts and Telemed ofVilnius, Lithuania.

By way of further exemplary detail, the housing 12 may define dimensionsof(L×W×H) of 42 mm×21 mm×11 mm. A Zero Insertion Force (ZIF) connectoris used to connect transducer arrays 14 and 16 to Doppler transducerelement 18. Multi-conductor cable 20 comprises a one centimeter-diametercable which exits the side of the housing 12. The elongated transducerarrays 14 and 16 each comprise piezoelectric arrays, includingsixty-four elements with an element pitch of 0.3 mm which operate at 7.5MHZ. Focal depth is 20 mm (although a variety of focal lengths may beprovided) and the elements possess about a 50–60% 6 dB bandwidth.Doppler transducer element 18 is also piezoelectric, includes apiezoelectric transmitter Tx and a piezoelectric receiver Rx andoperates at 5 MHZ, possessing greater than a 75% 6 dB bandwidth. Asingle piezoelectric element performing as both a transmitter andreceiver may also be used. The diameter of the combined transmitter andreceiver is 8 mm, and the focal depth is 20 mm (although, again, avariety of focal lengths may be provided). Doppler transducer element 18is oriented in housing 12 such that incident angle φ of Doppler beam 22is 30°.

The dual B-mode digital scan converter 78 takes image information fromthe beamformer 76 via a 34-pin ribbon cable and displays the informationon display device 82 in substantially real time. By “substantially realtime,” it is meant that image data from one array will be interleaved byhost computer 80 with data from the other array and displayedsimultaneously in a dual-panel, split-image format at 10–20 frames persecond per image.

The host computer 80 may comprise a specifically packaged personalcomputer having the ability to run a Microsoft Windows operating system,as well as appropriate ultrasound imaging software. The software ispreferably stored on a solid-state drive (Disk on Chip) as opposed to aconventional disc drive, in order to facilitate the boot-up andboot-down processes. It is currently believed that the minimum hardwarerequirements for host computer 80 include a Pentium 133 MHZ or betterprocessor, 32 MB of DRAM, 128 MB hard disk capacity, one RS-232 port,PCI Bus interface ports and a compatible video card, many of which arecommercially available from multiple sources.

As shown in FIG. 6, chirped Doppler hardware 86, if used in the systemof FIG. 5, includes a pre-amplifier 90 coupled to the Doppler transducerelement 18 of FIGS. 1A and 1B, a mixer 92, a low-pass filter 94, ananalog-to-digital converter 98 (“ADC”), a digital signal processor 100(“DSP”), a serial communication device 102 for interfacing the DSP 100to the host computer 80 of FIG. 5, a sweep generator 88 coupled to theDoppler transducer element 18 of FIGS. 1A and 1B and an attenuator 96.The Doppler transducer element 18 may, as previously noted, employchirped Doppler hardware 86 to convert depth information into thefrequency domain, allowing the user to obtain Doppler information atdiscrete depths which correspond to discrete frequency “bins.”Alternatively, a conventional pulsed Doppler technique may also beemployed. Data gathered by Doppler transducer element 18 is coded into abit vector and sent over an RS-232 port to host computer 80 where thebit vector is converted to a color vector indicative of blood flowdirection which is overlaid on top of longitudinal image 53 generated bylongitudinal transducer array 16 as processed by dual B-mode digitalscan converter 78.

As shown in FIG. 7A, one embodiment of pulsed Doppler hardware 186, ifused in the system of FIG. 5, includes gating and switching hardware 188coupled to the Doppler transducer element 18 of FIGS. 1A and 1B and to apre-amplifier 190, which, in turn, is coupled to dual mixers 192, eachof which are coupled to band pass filters (“BPF”) 194, these beingcoupled to an analog-to-digital converter 198 (“ADC”), a digital signalprocessor 200 (“DSP”) and a serial communication device 102 (see FIG. 6)for interfacing the DSP 200 to the host computer 80 of FIG. 5. TheDoppler transducer element 18 may, as previously noted, employ pulsedDoppler to obtain Doppler information at discrete depths. Data gatheredby pulsed Doppler transducer element 18 is coded into a bit vector andsent over an RS 232 port to host computer 80 where the bit vector isconverted to a color vector indicative of blood flow direction, which isoverlaid on top of longitudinal image 53 generated by longitudinaltransducer array 16 as processed by dual B-mode digital scan converter78.

As shown in FIG. 7B, another embodiment of pulsed Doppler hardware 286,if used in the system of FIG. 5, includes transmit/receive switchinghardware 288 coupled to two mutually separated groups of active imagingtransducer elements of longitudinal transducer array 16 (see FIG. 7C), atransducer driver/filter 290 for transmitting pulsed signals and an RFamplifier 292 for receiving reflected pulsed signals. The transducerdriver/filter 290 is coupled to and receives output from a controller294 and to a quadrature demodulator 296, which receives output therefromand which is also coupled to RF amplifier 292. Quadrature demodulator296 is coupled and outputs to analog-to-digital converter (“ADC”) 298,as does controller 294. ADC 298 outputs to digital signal processor(“DSP”) 299. DSP 299 is coupled to and communicates with ADC 298. DSP299 outputs to host computer 80 (see FIG. 5) through RS-232 driver 301.Data gathered by the two groups of active imaging elements acting aspulsed Doppler elements is manipulated as known in the art to provideblood flow direction and velocity data. The sign (positive or negative)of the output received from each channel, in association with relativemagnitudes of the signals, is used to determine blood flow direction.

Referring to FIG. 7C, longitudinal transducer array 16 suitable for usewith pulsed Doppler hardware 286 comprises a plurality of piezoelectricactive imaging elements 600, for example, sixty-four elements of 0.3 mmlength each, forming an array of 19.2 mm length. FIG. 7C is greatlyenlarged for clarity. Two groups A and B of elements 600, for example,seven elements 600 per group along a distance of 2.1 mm, are separatedalong the length of longitudinal transducer array 16 of, for example,6.9 mm. Each group of elements 600 is employed as a pulsed Dopplerelement configured to emit and receive ultrasound signals at the samebut opposing angle α, which may also be termed a “steering angle,” to aperpendicular P to the plane of longitudinal transducer array 16 inassociation with the hardware described above with respect to FIG. 7B.Angle α may comprise a relatively small angle, for example 12.2°. Itshould be noted that this implementation of the present invention may befabricated in a more compact form than those employing a separateDoppler element placed at the end of longitudinal transducer array 16,being as much as about 25% longitudinally shorter. Thus, for individualshaving short necks, and especially children and infants, thisimplementation may provide significant advantages with respect to easeof placement and use.

Referring now to FIGS. 8A through 8D and 9A through 9D, anotherexemplary implementation of the sensor assembly 10 of the presentinvention is employed in combination with a magnetic reference locationelement 300 to form, in combination, an ultrasonic cannulation assemblyof the present invention. In this variation, the elements of sensorassembly 10 are as previously described, with the exception of someaspects of cover 230. Elements and features previously described hereinare identified by the same reference numerals in FIGS. 8A through 8D.Cover 230 is sized to conformally fit over housing 12 (not shown), whichhas been snapped into frame element 46 (see FIG. 4) associated withelongated, flexible flexible, protective, transparent sheath 44 aspreviously described. Housing 12, which is placed inside elongated,flexible, protective, transparent sheath 44 over a mass of acoustictransmission gel is snapped into frame element 46, which is placedopposite the bottom of housing 12 on the outside of sheath 44. Cover 230is then placed over housing 12 from the outside of the sheath 44 andsnap-fit to frame element 46. Cover 230 includes wings 240 extendinglaterally from opposing sides thereof, each wing 240 carrying a magnet242 disposed and secured in a downwardly facing cavity 244 thereof. Itis currently preferred to use Neodymium magnets, offered by JobmasterMagnets of Randallstown, Maryland. Wings 240 are preferably formed asintegral portions of cover 230, curve arcuately away from the sides ofcover 230 (see FIG. 8B) and are sized in length and cross-section topermit upward and downward flexing (see arrows) to accommodate differentneck circumferences. Gripping elements 246, to facilitate gripping bythe hands of the clinician for manipulation of sensor assembly 10, arelocated on each side of cover 230. In this embodiment, arrows on the topof cover 230 (see FIG. 8A), which may be respectively colored red (forarterial flow) and blue (for venous flow), indicate direction and typeof blood flow. Cover 230 also includes a vertical slit 250 (see FIG.8B), which facilitates ejection of sensor assembly 10 therefrom afteruse and defines a notch comprising needle guide 40, which, whenassembled with frame element 46, is coincident with a notch formedtherein. Arrows on the end of cover 230 (see FIG. 8B) point towardneedle guide 40.

As shown in FIGS. 9A through 9D, reference location element 300comprises a film or tape 302 having an adhesive 304 thereon, adhesive304 being covered by tape backing 306 which includes folded portion 306a to facilitate gripping thereof when it is desired to remove tapebacking 306 for application of film or tape 302 to the neck or locationon the body of a patient. Film or tape 302 comprises a sandwich orlaminate of two individual films coated on their facing surfaces withadhesive. Within the sandwich or laminate are disposed two metal discsor flexible polymer elements 310 of a magnetically sensitive orresponsive material, such as zinc-plated steel shim stock; metal discsor flexible polymer elements 310 being symmetrically located on eachside of centerline CL of magnetic reference location element 300. Recessor cutout 312 at the periphery of film 302, which will be orientedtoward the patient's head in use, facilitates needle insertion withouthaving to penetrate film 302.

Of course, magnets 242 may be placed on magnetic reference locationelement 300, while metal discs or flexible polymer elements 310 may beplaced on cover 230, such arrangement being encompassed by the presentinvention. Furthermore, a magnetic tape comprising the aforementionedflexible polymer and in the form of an anisotropic conductive film, suchas is used in refrigerator magnets, may be used in lieu of discretemagnets.

In use, the sensor assembly 10, secured within elongated, flexible,protective, transparent sheath 44 and having cover 230 placed thereover,is placed over magnetic reference location element 300, which has beenadhered to the patient by pulling tape backing 306 off of adhesive 304and applying film 302 to the patient, adhesive-side down. An acoustictransmission gel has been placed over the outer surface of film 302, andsensor assembly 10 is placed over reference location element 300 witheach of magnets 242 at least partially superimposed over one metal discor flexible polymer elements 310, which is sized in diameter slightlylarger than magnets 242. Due to the magnetic attraction between magnets242 and metal discs or flexible polymer elements 310, sensor assembly 10is held firmly in place. However, the magnetic attraction is limited sothat sensor assembly 10 may be moved laterally or vertically overreference location element 300 to position it precisely as previouslydescribed and for the purposes previously indicated.

It is also contemplated that other approaches for locating a sensorassembly on the patient are possible and encompassed by the presentinvention. For example, hook and loop fabrics, such as those offered byVelcro Corporation may be employed. In one configuration, a collar forplacement about the neck of a patient may be fabricated using, forexample, a loop fabric on the exterior thereof and the sensor assemblymay be provided with one or more patches of hook fabric for engaging theloop fabric of the collar to place, adjust and secure the sensorassembly to the collar. Alternatively, discs of loop fabric may beadhered to the skin of the patient and patches of hook fabric placed onthe sensor assembly to place, adjust and secure the sensor assembly tothe discs.

Further, while the present invention has been discussed for the sake ofconvenience in relation to cannulation of blood vessels, it iscontemplated to have equal utility in placement of nerve blocks. Forexample, if it is desired to block the brachial plexus (a network ofnerves formed by spinal nerves C5 to C8 and T1 with contributions fromC4 and T2, which constitutes the entire nerve supply for the upperextremities, as well as a number of neck and shoulder muscles), thesensor assembly of the present invention may be used to visualize theadjacent artery and vein and to avoid the artery, vein and nerve bundlewhile placing the needle tip next to the nerve to initiate the block.Thus, the scope of the present invention encompasses the location ofblood vessels for reference and locational purposes, regardless ofwhether the blood vessels or some other structure inside the body is ofinterest as a target location.

Referring now to FIGS. 10A through 10D of the drawings, an inventiveembodiment 400 of elongated, flexible, transparent protective sheath 44is depicted. As shown in FIG. 10A, inventive sheath 400 may comprise alow-density polyethylene polymer film defining a substantially tubularbody 402 and having a closed end 404 and a first open end 406. Ifdesired, tubular body 402 of sheath 400 may taper from a relativelysmaller cross-section proximate closed end 404 to a relatively largerfirst open end 406, but this is not required. In preparation forultimate use and for packaging, tubular body 402 is everted, or turnedinside-out, by drawing first open end 406 back over the exterior surface408 thereof until everted first open end 406 lies proximate the closedend 404 as shown in FIG. 10B, so that a portion of the former interiorsurface 410 of sheath 400 now lies on the exterior thereof and a secondopen end 412 is created at the opposite end of everted sheath 400 fromclosed end 404 and first open end 406. The polymer film at second openend 412 is then rolled outwardly over the doubled polymer film to form atoroidal shape 414 of rolled, doubled polymer film until a locationproximate the closed end 404 is reached, leaving a pouch 416 surroundedby a skirt 418 of polymer film comprising everted first open end 406, asshown in FIG. 10C. Skirt 418 is then folded back over the toroidal shape414 of rolled, doubled polymer film, the resulting structure being shownin FIG. 10D. As also shown in FIG. 10D, the resulting structure may beplaced in a cavity 500 in a tray 502 with the upper mouth 420 of thefolded-back skirt 418 facing upwardly, as is the lower mouth 422 oftoroidal shape 414 of rolled, doubled polymer film opening into pouch416. The tray 502, with sheath 400, frame element 46, cover 230,reference location element 300, sterile acoustic transmission gel,cotton gauze pads, cotton swabs, user guide and cautionary statement, isthen packaged and sterilized, as known in the art. At the surgicaltheatre or other location of use, a sensor assembly 10 may be easilyinserted into sterile pouch 416 by an individual after disposition ofacoustic transmission gel therein as previously discussed, after whichanother individual may grasp the lower mouth 422 of folded-back skirt418 proximal to upper mouth 420 and pull sheath 400 back to extend italong and over multi-conductor cable 20, the sterility of the exteriorof sheath 400 thus being maintained free from potential contamination bythe nonsterile sensor assembly 10 and multi-conductor cable 20 on theinterior thereof. The extension of the sheath 400 may be facilitated byaffixing two tabs 424 of, for example, paper, cardboard or a polymerproximate the edge of folded-back skirt 418, the tabs being affixed atopposite sides of the edge of folded-back skirt 418. The tabs 424, whichmay be brightly colored to aid visibility, aid the individual who graspsand extends the sheath 400 by providing an easily seen visual landmarkor reference point on an otherwise transparent and featureless edge offolded-back skirt 418. It is envisioned that the individual who extendssheath 400 may place the thumb and forefinger of each hand,respectively, on a pull tab 424, grasping the pull tabs 424 adjacent theedge of folded-back skirt 418 and gently pulling in order to extendsheath 400. Sterile frame element 46 and cover 230 may then be assembledwith housing 12 of sensor assembly 10 and a procedure performed, aspreviously described. Of course, the protective sheath 400 is notlimited to use with the inventive sensor assembly 10 of the presentinvention, but may be employed with any sensor introducible thereinto.

Although the present invention has been described with reference toparticular embodiments, the invention is not limited to these describedembodiments. Rather, the invention is limited only by the appendedclaims, which include within their scope all equivalent devices ormethods that operate according to the principles of the invention asdescribed.

1. A kit of disposable components assembled in combination with anondisposable sensor assembly including a housing carrying at least onetransducer, the combination comprising: an elongated, flexibleprotective sheath having an open end and a closed end, the housingdisposed within the flexible protective sheath proximate the closed endthereof; a frame element configured to engage at least a portion of thehousing and engaged therewith with a portion of the flexible protectivesheath disposed between the housing and the frame element; and markingson an exterior surface of the combination associated with the housingand indicative of two opposing directions of blood flow.
 2. A kit ofdisposable components assembled in combination with a nondisposablesensor assembly including a housing carrying at least one transducer,the combination comprising: an elongated, flexible protective sheathhaving an open end and a closed end, the housing disposed within theflexible protective sheath proximate the closed end thereof; a frameelement configured to engage at least a portion of the housing andengaged therewith with a portion of the flexible protective sheathdisposed between the housing and the frame element; and a set oflongitudinal grid markings and a set of cross-sectional grid markingsperpendicular to the set of longitudinal grid markings on an exteriorsurface of the combination associated with the housing.
 3. A kit ofdisposable components for use with a nondisposable sensor assemblyincluding a housing carrying at least one transducer, the kitcomprising: an elongated, flexible protective sheath having an open endand a closed end; a frame element configured to engage at least aportion of the housing; and a reference location element configured tobe secured to skin of a patient and for cooperative placement of thehousing thereover for movable affixation of the sensor assembly thereto.4. The kit of claim 3, further comprising a quantity of sterile acoustictransmission gel, cotton gauze pads, cotton swabs, user guide andcautionary statement.
 5. The kit of claim 3, further including: a pairof wings secured to the frame element and extending extending laterallyfrom opposing sides thereof, the wings each bearing a magnetic elementcomprising one of a magnet and a magnetically sensitive material; andwherein the reference element further comprises: a film or tape havingan adhesive thereon; and a pair of magnetic elements comprising anotherof a magnet and a magnetically sensitive material affixed to the film ortape at spaced locations thereon.
 6. A kit of disposable components foruse with a nondisposable sensor assembly including a housing carrying atleast one transducer, the kit comprising: a frame element configured toengage at least a portion of the housing; and an elongated, flexibleprotective sheath having an open end and a closed end wherein theelongated, flexible protective sheath further comprises: a singletubular body of polymer film configured in a toroidal shape comprising arolled double layer of polymer material defining a closed end pouchextending transversely thereto on one side thereof and a skirt ofpolymer film extending on a foot side of the toroidal shape from aninterior of the toroidal shape about an exterior of the toroidal shapeand extending transversely thereto on another side of the toroidal shapeopposite the closed end pouch; and the kit further comprises a trayconfigured to support the flexible protective sheath with the closed endpouch resting therein and the skirt facing upward.
 7. The kit of claim6, further comprising a quantity of sterile acoustic transmission gel,cotton gauze pads, cotton swabs, user guide and cautionary statement. 8.A protective sheath for use in enclosing a nonsterile sensor element andin a packaged configuration, comprising: a tubular body comprising apolymer film and having a closed end and a first open end; the firstopen end being everted back over a portion of the tubular body until theeverted, first open end is proximate the closed end to provide a doubledlayer of polymer film and a second open end; wherein the doubled layerof polymer film is rolled outwardly from the second open end, forming atoroidal shape with a foot comprising the closed end extendingtransversely therefrom and a skirt of polymer film defining the evertedfirst open end extends about an outer periphery of the toroidal shape onan opposite side thereof from the foot.
 9. The protective sheath ofclaim 8, further including at least one pull tab secured to the skirt ofpolymer film proximate the everted first open end.
 10. A protectivesheath for use in enclosing a nonsterile sensor element and in apackaged configuration, comprising: a single tubular body of polymerfilm configured in a toroidal shape comprising a rolled double layer ofpolymer material defining a closed end pouch extending transverselythereto on one side thereof and a skirt of polymer film extending on afoot side of the toroidal shape from an interior of the toroidal shapeabout an exterior of the toroidal shape and extending transverselythereto on another side of the toroidal shape opposite the closed endpouch.
 11. The protective sheath of claim 10, further including at leastone pull tab secured to the skirt of polymer film.
 12. A method ofconfiguring a protective sheath for use in enclosing a nonsterile sensorelement, comprising: providing a tubular body comprising a polymer filmand having a closed end and a first open end; everting the first openend back over a portion of the tubular body until the everted first openend is proximate the closed end to provide a doubled layer of polymerfilm and a second open end; rolling the doubled layer of polymer filmoutwardly from the second open end to form a toroidal shape with a footcomprising the closed end extending transversely therefrom; and pullinga skirt of polymer film defining the everted first open end about anouter periphery of the toroidal shape to lie on an opposite side thereoffrom the foot.
 13. The method of claim 12, further comprisingintroducing a sensor element having a cable element extending therefrominto the foot through a mouth defined by the skirt of polymer film andthrough the toroidal shape and pulling the skirt of polymer film alongthe cable element to extend the protective sheath therealong from thesensor element located in the foot.
 14. The method of claim 12, furthercomprising pulling the skirt of polymer film using, at least in part, atleast one pull tab secured to the skirt of polymer film proximate theeverted first open end.